The compounds of choice, before the invention herein, for providing curable thermosets, have been cycloaliphatic diepoxides containing a primary oxycarbonyl linkage and these have been generally formulated with anhydride curing agent, initiator and catalyst for thermal curing to provide an insoluble, infusible cured thermoset. The compounds have low viscosity and are therefore easily manipulated in the uncured state. The cured compositions adhere well to electronic components, have good durability, provide good insulation of adjacent metal lines from each other, provide good vibration and shock resistance, and have low moisture absorption characteristic. The disadvantage of the cured compositions is their intractability. They are very difficult or impossible to remove from microelectronic assemblies. Their decomposition temperatures are very high.
With the increase in chip size and the common employment of multiple chip modules and the increased cost of the electronic packaging, it has become desirable to recover operative components from assemblies which are inoperative. This is not practical where the compounds now in commercial usage are the basis for the cured compositions which provide encapsulation and underfill for the components. The very high decomposition temperatures of the cured compositions exclude thermal decomposition as a practical method for removing encapsulation and underfill composed of the cured compositions.
Thus, there has been an ongoing search for resins for providing cured thermosets for encapsulation and underfill for electronic components that will allow repair, replacement, recovery or recycling of operative electronic components from assemblies which have become inoperative. The cured thermoset which is being sought is referred to in the art as being "reworkable."